Each power device typically comprises a chip of semiconductor material, on which one or more power components (e.g., power transistors—such as vertical structure MOS power transistors) are integrated, and a package wherein the chip is embedded for protecting it and allowing the access to terminals thereof.
As it is known, the power components, being affected by high voltages and/or high currents (of the order of 50-1500V and 0.1-8A, respectively), are subject to considerable heating during operation. For this reason, the power device needs a package that, for ensuring adequate heat dissipation properties (so as to avoid overheating phenomena to the chip that may cause malfunction or breakage), is equipped with one or more heat-sinks for dissipating to the outside the heat generated by the chip during operation thereof.
An example of such a package is represented by the package of the “DSC” (“Dual Side Cool”) type, which is provided with two different heat-sinks. In particular, each power device with DSC package (or DSC power device) comprises a lower heat-sink that extends between a conductive region of the chip (e.g., a drain terminal of the power transistor) and a mounting surface of the package that, in use, typically faces towards a support (such as a printed circuit board—or PCB) on which the power device is mounted, and an upper heat-sink than extends between another conductive region of the chip (e.g., a source terminal of the power transistor) and a free surface of the package (typically opposite the mounting surface).
The power devices are typically used in switching circuits, for example for converting a direct voltage into an alternate voltage. A very widespread switching circuit is implemented by a full-bridge configuration, which generally comprises two pairs of power transistors in a half-bridge configuration for differentially driving a load; in particular, the power transistors of each pair are arranged in series, i.e. they are connected between a reference terminal, or ground, and a supply terminal (with a common terminal that usually defines a corresponding output terminal), whereas the two pairs of power transistors are arranged in parallel (i.e. they share the ground and supply terminals), with the load being connected between the respective output terminals.
A DSC power device is known in the art which comprises a single package within which two power transistors are housed (each one integrated on a respective chip) in half-bridge configuration (double-island DSC power devices), or an upper power transistor of the half-bridge (or upper transistor) and a lower power transistor of the half-bridge (or lower transistor). In general, in the double-island DSC power device the power transistors are in a mutually reversed configuration, i.e. the drain terminal of one of the two power transistors (for example, of the lower transistor) is connected together with the source terminal of the other power transistor (for example, the upper transistor) to the lower heat-sink (that usually acts also as a lead for accessing the output terminal), whereas the remaining source and drain terminals, respectively, are connected to corresponding mutually insulated upper heat-sinks.
In this way, compared to the traditional solutions wherein each power device comprises a package in which a single power transistor is housed, reduced size of the half-bridge are obtained, and thus more compactness and making simplicity of the corresponding switching circuit.
However, the double-island DSC power devices, as including two power transistors within them, are more affected by overheating problems.
In this regard, the use of auxiliary heat-sinks (for example, external to an insulating body of the package) for increasing heat dissipation from the chip could involve some drawbacks. In particular, to adopt (as the state of the art would suggest) two external heat-sinks each one mounted on a respective upper heat-sink (in order to avoid short-circuits between the terminals of the power transistors connected to such upper heat-sinks) would involve significant imbalances in the heat dissipation of the power transistors (due, for example, to inevitable manufacturing asymmetries and/or misalignment in the positioning of such external heat-sinks).